Numerical Simulation of Water Mist Suppression of Tunnel-fire Scenarios

Water-mist fire suppression systems offer a number of potential advantages over conventional sprinkler systems. A water-mist system uses very fine droplets of around 50μm diameter, which results in entirely different behaviour. In particular the water-mist remains suspended in air for long periods, and is influenced by the airflows caused by the fire and the general ventilation regime. In order to better understand the processes involved, a numerical model has been developed that models the effect of a water-mist fire suppression system on a typical tunnel fire scenario. A commercial available CFD package (fluent) is used. In this model, the water-mist is represented by a discrete phase model and the fire is modelled with a non-premixed combustion model. For simplicity a propane fire was used. Initial results show behaviour consistent with real fires and experiments. However limitations of the combustion model have been identified, which limit its suitability for this scenario.